How do I use silver dust, do I mix it with something else?
Are you talking about the little tube of edible dust you can get at Hobby Lobby? If we're thinking of the same thing, I poor a little vanilla in a tablespoon and tap some dust into the spoon and stir around. The amount of dust I add depends on how thick I want my shimmer. I then paint the mixture onto the fondant or gumpaste I'm working with.
If you're using luster dust or pearl dust, I'd recommend using vodka or lemon extract, as there is a high alcohol content to both, and then the liquid will evaporate and leave your fondant in good condition. Liquid that is higher in water content will make your fondant sticky and take a lot longer to dry.